Studies will be continued on the changes in metabolism during embryological development in sympathetic ganglia and dorsal root ganglia of chicken embryos. Observation on glucose metabolism will be guided and interpreted with the aid of a new mathematical model of the metabolism of 14C from specifically labeled glucose. This new model utilizes the time course of isotopic equilibration as a source of information and avoids certain inapplicable assumptions of models previously published by other investigators. Measurements will include release of the 14C to CO2 and to lactate, as well as incorporation of 14C into tissue constituents. The rate of lipid synthesis will also be studied as a function of age, by measuring incorporation of labelled precursors into lipids in embryonic ganglia. Comparison of changes during development in the rates of lipid synthesis with the changes in various aspects of glucose metabolism should improve the understanding of relationships between these two aspects of metabolism. In addition, the applicability of our new approach to carbohydrate metabolism, in studies on other tissues and tissue cultures, will be explored, as opportunities for collaborative feasibility studies with other investigators arise.